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Hi guys, I need to solve this 3rd order ODE:

?⃛+2??̈+3??̇+4??=2, t≥0, ?̈(0)=?̇(0)=?(0)=0

This is my script:

[t,y] = ode45(@diffeq3,[0 50],[0;-1;1]);

plot(t,y)

function dy = diffeq3(t,y)

if t >= 0

dy(3) = 0

dy(2) = 0

dy(1) = 0

end

dy = zeros(3,1);

dy(1) = y(2);

dy(2) = y(3);

dy(3) = 2 - 2*y(3) - 3*y(2) - 4*y(1);

end

Did I do it right?

I got two questions, I got three curves which on is which?

And did I define t≥0, ?̈(0)=?̇(0)=?(0)=0 correct? With:

if t >= 0

dy(3) = 0

dy(2) = 0

dy(1) = 0

Thanks in advance for the help!

Star Strider
on 10 May 2020

There appears to be a factor of ‘y(1)’ missing in the last 3 terms of the ‘dy(3)’ equation. (I gave your differential equation as posted to the odeToVectorField function to be certain.)

Also, the if block is not necessary. It does nothing, and produces slower code.

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